Wang et al, in copending U.S. application Ser. No. 231,859 filed Feb. 5, 1981 now U.S. Pat. No. 4,355,062 have disclosed a new class of bis(hydroxyalkyl)disiloxanes which are useful as additives or dopants for methyl alkyl siloxanes employed as lubricants for capacitive electronic discs. These additives or dopants are made by reacting dichlorodialkylsilanes with a heterocyclic ethylene oxide, such as tetrahydrofuran, heating the product in the presence of an alkali metal to form a 1-oxa-2-silacycloalkane, and hydrolyzing this last product in the presence of an acidic catalyst, such as HCl, to form a bis(hydroxyalkyl)disiloxane.
In order to successfully employ these disiloxane dopants or additives in lubricants for capacitive electronic disc manufacture, they must be highly purified, particularly to remove volatiles and other impurities that would change the chemical composition or the rheological properties of the doped lubricant on the surface of the disc with time. Accordingly, the dopant has heretofore, both commercially and as disclosed in U.S. application Ser. No. 231,859 now U.S. Pat. No. 4,355,062 referred to hereinabove, been molecularly distilled by the "falling film" type of molecular distillation at approximately 100.degree. C. and about 2.times.10.sup.-3 Torr to purify the dopant and to remove low molecular weight materials including HCl, alcohols and unreacted oxasilacycloalkanes.
However, molecular distillation, particularly of the "falling film" type which is presently commercially used and the type successfully employed in above-referred to U.S. application 231,859 now U.S. Pat. No. 4,355,062, is time consuming and expensive. This type of distillation can process only about 11/2 liters of raw material per week, or one drop every 12 seconds; and requires close supervision because the temperature versus the pressure is very critical to obtain a good product. Additionally, the equipment must be carefully monitored for leaks since contamination from the atmosphere reaching the hot distilling liquid may result in thermal degradation of the product.
For a material to be useful as a capacitance electronic disc lubricant additive or dopant, it must meet very stringent specifications. These specifications require that the material have a molecular weight of approximately 530; a viscosity at 25.degree. C. of 210.+-.30 centipoises; less than 10 ppm of inorganic purities; must be free of particulates; must have an infrared absorption characteristic close to the ideal; an optical density for a 1.0 centimeter path of less than 0.1 at 400 nm and 0.3 at 300 nm; a refractive index at 25.degree. C. of approximately 1.4620; and must be free of volatiles at 10.sup.-6 Torr and 22.degree. C. or at 1 atmosphere and 37.7.degree. C.